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Патент USA US3099722

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United States Patent 0 ”
3,099,712
Patented July 30, 1963
1
2
3,099,712
receiver in precise synchronism with those of the trans
mitter.
The use of an interlaced pattern improves the vertical
SYNCHRONIZING ClRtIUlT
Larnetl A. Meacham, New Providence, NJ, assignor to
Bell Telephone Laboratories, Incorporated, New York,
N.Y., a corporation of New York
Filed .lune 6, 1969, Ser. No. 34,263
8 Claims. (Q1. 178-695)
This invention relates to synchronization signal genera
tors and, more particularly, to economical interlaced tele
vision scanning signal generators.
resolution of the resulting picture by a factor of two with
out adding any further burden to the transmission system.
A simple and inexpensive circuit for taking advantage of
this fact is therefore highly advantageous in such ?elds of
application as closed circuit television and videotelephony,
where low cost is commonly a prime objective. The
10 present invention meets this requirement.
These and other objects and features, the nature of
the present invention and its various advantages, will be
In order to generate interlaced television scanning sig
nals, it is conventional practice to generate vertical and
more readily understood upon consideration of the at
horizontal scanning pulses having a ?xed ratio between
tached drawing and of the following detailed description
their respective repetition rates. If this ratio is kept with 15 of the drawing.
in narrow limits of any member of a large class of suit
In the drawing:
able numerical values, the generation of an interlaced
FIG. 1 is a schematic diagram of a television synchroni
pattern or raster is possible by well~known scanning pro—
zation signal generator providing 2:1 interlace accord
cedures. One obvious way in Which to generate pulses
ance with the present invention; and
‘having a ?xed ratio is to obtain the pulses themselves by
FIG. 2 comprises graphical representations of various
frequency division or count-down techniques. While this
waveforms useful in the description of FIG. 1.
method can provide almost absolute assurance of a proper
Referring more particularly to FIG. 1, there is shown
interlace, it has the disadvantage of requiring a large
a schematic diagram of a television scanning signal gen
amount of circuitry with the attendant penalties of higher
erator comprising a horizontal oscillator 18, a limiting,
cost and lower reliability.
25 phase splitting ‘and differentiating network 11, a bistable
Another method of generating an interlaced pattern,
gate circuit 12, and a vertical oscillator 13. Horizontal
the so-called “random interlace” technique, calls for the
oscillator 10 comprises a tank circuit 14 and an n-p-n
separate generation of horizontal and vertical scanning
transistor 15 having a base electrode 16, a collector elec
pulses. In order to generate an approximation of a 2:11
trode 17 and an emitter electrode I18‘. Tank circuit 14
interlaced pattern with this technique, it is necessary that
includes a capacitor 19 and a tapped inductor element 20.
the independent frequencies of the vertical and horizontal
The base 16 of [transistor 15 is connected through biasing
oscillators be respectively stabilized to a high degree of
diode 22 to the upper tap of inductor 20. Emitter elec
accuracy. This requirement is not di?icult to meet for
trode 18 of transistor 15 is connected through a negative
the horizontal oscillator. A 'vertical ‘oscillator, how
feedback resistor 21 to the lower tap 23 of inductor 20.
ever, which has a relatively low frequency, presents a very 35 Base 16 is biased by diode 22, supplied with current
dii?cult design problem for the order of precision re
through resistor 24 from source 27, to cause transistor 15
quired. - Resulting structures are usually bulky, compli
to :operate in a linear portion of its operating charac
cated and costly.
teristic: Diode 22, preferably of silicon, affords a stable
-It is an object of the present invention to reduce the
bias potential of about 0.6 volt, while presenting a low
cost and complexity of television synchronizing signal 40 alternating current impedance to signal currents.
generators while maintaining good scanning resolution.
Oscillator it] operates with bridge-stabilized oscillator
It is a more speci?c object of the invention to produce
a locked 2:1 inter-lace of a television scanning pattern
with simple, inexpensive circuit components.
In accordance with the present invention, horizontal
and vertical scanning pulses are produced at their ap
proximate respective repetition rates with simple, inex
pensive oscillators. These oscillators are coupled together
by utilizing the horizontal oscillator output as an ancillary
timing wave to trigger the vertical oscillator. In order to
insure a proper 2:1 intenlace regardless of the actual fre
quency ratio of the horizontal and vertical outputs, the
horizontal output used as a trigger for the vertical oscilla
action as disclosed in the copending application of the
present applicant and F. West, Serial Number 759,474,
?led September 8, 1958, by which oscillatory voltages
induced in tank circuit 14 by currents drawn through
emitter 18 and negative feedback resistor 21 \are applied
to base 16 via biasing device 22. Limiting device 25 is
connected in shunt with a portion of inductance 20; this
device limits the amplitude of voltage across the tank
circuit, and thus prevents transistor 15 from saturating
or cutting oif at the extremes of the voltage swings.
Limiting device 25 is illustrated in FIG. 1 as a semi-con
ductor varistor but may, of course, comprise any other
nonlinear resistive element such as a thermistor, the
tor is shifted in phase by 180 degrees after each cycle of
the vertical oscillator.
55 resistance of which decreases with rising power dissipa
This phase shift in the triggering wave causes the verti
tion therein.
cal oscillator to be triggered at the end of each (n+1/2)
The waveform of current vdrawn through collector 17
complete cycles ‘of the horizontal oscillator regardless of
of transistor 115 is illustrated in FIG. 2 as waveform (a).
their respective natural frequencies, :11 being an integer.
As can be seen, this wave form is a sine :wave having a
That is, if n is the instantaneous integral ratio of the
frequency determined by tank circuit 14. In the illus
respective period durations of the two oscillators, with
trative circuit this frequency has been selected as 15,750
intercoupling but without the phase reversals, the circuits
cycles per second. [Changes in the temperature and other
of the present invention cause the vertical oscillator to
operating conditions of oscillator .10 will, of course, vary
be triggered at a half cycle earlier or later than this ratio
would normally dictate. Since the “1/2” term always pro 65 this frequency to some extent.
vides an accurate 2:1 interlace, the actual Value of n can
vary from time to time over a moderate range without
impairing the interlace of the scanning pattern.
While the present disclosure gives attention primarily
to scanning waveforms in a television transmitter, it is
assumed that techniques well-known in the art are to be
used to control corresponding Waveforms of ‘an associated
Collector #17 is connected to one end of the primary
winding of a phase splitting transformer 26. The other
end of :the primary winding of transformer 26 is con
nected to voltage source 27 to provide the operating volt
age for collector 17 of transistor \15. A second limiting
device 28 is ‘connected directly across this primary wind
ing. The sinusoidal oscillatory collector current of tran
3,099,712
3
4
sister 15 thus produces a sharply limited voltage wave
form across the primary winding of transformer 26. This
resulting waveform is illustrated as waveform (e) in
square wave is applied by way of lead 29 to terminal 30
FIG. 2.
Vertical oscillator 13 comprises a p-n-p transistor 53
having a base electrode 54, an emitter electrode 55 and a
collector electrode 56‘. Base electrode 54- and emitter
‘and serves as a timing Wave for the horizontal scanning
electrode 55 are coupled together by way of transformer
operation in a television transmitter, not shown.
The resulting current in the primary winding of trans
former v26 produces in the secondary windings steeply
rising pulses of voltage each time the primary current
changes direction. Furthermore, these pulses are equal
57 to provide blocking oscillator action. That is, a rise
in voltage at emitter 55, caused by a voltage increase at
base 54, is coupled by way of transformer 57 back to base
54.- and thus further increases the voltage at base 54. This
regenerative action continues until transistor 53 is satu
ly spaced and alternately of opposite polarity, since
rated and no additional current flow can be maintained
waveform is illustrated in FIG. 2 as waveform (b), and
can be seen to comprise essentially a square wave.
The
by emitter 55. Saturation of the transistor persists until
the current in the primary winding alternately reverses its
a timing capacitor ‘63, connected between the lower pri—
direction.
As illustrated in FIG. 1, the center tap 31 of the sec 15 mary terminal of transformer 57 and ground, is dis
180 degree phase difference. The pulses appearing at
the upper end of the secondary winding of transformer
charged to a point at which inadequate voltage remains
across the transformer windings to sustain this condition.
At this point the regenerative action reverses and abruptly
cuts off the transistor. The impedance of transformer 57,
effectively terminated by resistors 60‘ and 61 when the
base-emitter impedance is low, serves to limit the current
26' are differentiated by capacitor 32 and resistor 33 to
form a train of pips, illustrated in FIG. 2 as waveform
tion.
ondary winding of transformer 26 is connected to ground
potential. This transformer therefore acts as a phase
splitter to produce waveforms at the two extremities of
its secondary winding which are identical except for a
in the collector-emitter path of transistor 53 during saturaL
‘ .
A variable resistor 59, connected in the emitter circuit
(c); these pips are applied by way of resistor .34 to the
base 35 of a transistor 36. Similarly, the pulses appear 25 of transistor 53, serves in association with capacitor 63
ing at the lower end of the secondary winding of trans
to determine the frequency of the vertical oscillator.
That is, when transistor '53 is cut off following a period
former 26 are differentiated by capacitor 37 and resistor
38 to form pips illustrated in FIG. 2 as waveform (d),
of saturation as described, the timing capacitor ‘63- grad
ually builds up a charge. Current is supplied to ca
and these are applied by way of resistor 39' to the base
pacitor 63 from source 27 through variable resistor 59.
'40 of a transistor 41.
When the voltage on capacitor 63 reaches a level almost
The collector 44 of transistor 36‘ is coupled to the base
40 of transistor '41 by way of a voltage divider compris
su?icient to forward bias emitter 55, transistor 53 is
triggered into conduction by a pulse applied to base 54
ing resistors 38 and 3§ and a resistance-capacitance net
through a coupling capacitor 62 and the charge accumu
work 45. Similarly, the collector 42 of transistor 41 is
lated on capacitor 63 is again rapidly ‘discharged through
coupled to the base 35 of transistor 36 by way of a
the primary winding of transformer 57 and the col
voltage divider comprising resistors 33 and 34 and a
resistance-capacitance network 43. The emitter 46 of
lector-emitter path of transistor 53. The resulting
transistor 36 and the emitter d7 of transistor 41 are con
waveform across capacitor 63 is applied to terminal 64
and appears as waveform (g) in FIG. 2. This wave
form serves as the vertical sweep voltage for a television
nected together and coupled through a resistor 4-8 to
ground potential.
Transistors 36 and 411 are cross-coupled so as to form
a bistable circuit in which only one of the two transistors
is permitted to conduct at a time. That is, when tran
transmitting apparatus, not shown.
sistor 36 begins to conduct, a voltage is coupled by way
this ‘occurs is determined jointly by the gradual voltage
transistor 41 off. Similarly, when transistor ‘4]. begins
to conduct, a voltage is coupled by way of network 43
64} and 61 and the voltage pulses at point 52.
to the base 35 of transistor 36' to cut transistor 36 off.
Either of these transistors will continue to conduct until
a change to the opposite stable state is induced by an
three superimposed components is illustrated in FIG. 2 as
As noted above, transistor 53 begins to conduct when
emitter 55 becomes forward-biased. The instant at which
of network 45 to the base 40 of transistor 41 to cut 45 increase on capacitor ‘63, the bias established by resistors
external signal.
Load resistors 49, 50 and 51 connect the collectors of
transistors 36 and ‘4-1 to voltage source 27 and have values
The base-emitter voltage waveform resulting ‘from these
waveform (1‘). As shown in FIG. 2, when the magnitude
of this voltage exceeds a threshold level 65, corresponding
to zero base-emitter potential, transistor 53 will begin to
conduct. The regenerative action immediately takes ef
fect, the voltage accumulated on capacitor 63‘ is rapidly
discharged through transistor 53 and transistor 53 cuts off
chosen to permit transistors 36 and 41 to operate in their 55
again.
linear range when in the conducting condition. That is,
A ‘diode 66 is connected across the emitter winding of
the voltage biases applied to transistors 36 and ‘41 are of
transformer 57 to quench oscillation of the transformer
such magnitudes as to prevent saturation when these
following the regenerative action. This is done to avoid
transistors are in the On condition.
Bistable circuit 12 is caused to shift between its two‘ 60 objectionably large transient voltages across transistor 53,
and also to dissipate stored energy in transformer 57
stable states of operation by means of voltage pulses
which might otherwise cause the durations of successive
applied to the upper end of resistor 48. These voltage
periods of oscillator 13 to be interdependent. In physical
pulses are of proper polarity and of suf?cient magnitude
embodiments, it has been found preferable for the value
to‘cause the particular one of transistors 36 and 41 which
is‘ in the conducting state to be cut off and thus to initiate 65 of the integer n to vary randomly, as opposed to varying
systematically from cycle to cycle.
conduction in the other transistor by way of one of the
The voltage appearing at the collector 56 of transistor
cross-coupling networks.
53, shown as waveform (h) in FIG. 2, is applied to termi
When transistor 36 is in the On state, waveform (c),
nal 67 to provide the vertical blanking pulses for televi
appearing at the upper end of resistor 33, is coupled by
sion transmitting apparatus, not shown. These pulses are
way of transistor 36 to point ‘52. When transistor 41 is 70 also coupled by way of coupling capacitor 68 to the upper
in the On condition, waveform (d), appearing at the
end of resistor 48 and are there used to trigger bistable
lower end of resistor 38 is coupled by way of transistor
circuit :12 ‘between its two stable states.
{1 to point 152. As transistors 36 and 41 are alternately
From the above description it can be seen that horizon
turned on and cut off, the waveform at point 52 shifts
tal scanning pulses generated in oscillator 10 are split in
between the waveform (c) and the waveform (d). The 75 phase and differentiated by transformer 26, with the as
3,099,712
6
5
2. Means for generating interlaced television scanning
sociated capacitors and resistors 32, 33, 34 and 37, 38, 39.
signals comprising a free-running source of horizontal
Bistable circuit 12 alternately selects the two phases of
these differentiated pulses after each cycle of the vertical
synchronizing pulses, means for shifting the phase of
said horizontal synchronizing signals in integral sub
oscillator and applies them to oscillator 13 as auxiliary
triggering pulses. Vertical oscillator 13 therefore always
triggers after an odd number of half cycles of the hori
multiples of 360 degrees, a triggerable source of vertical
zontal oscillator. The ratio of frequencies of oscillators
13 and 10 is thus always equal to (n+1/2), regardless of
the actual values of these frequencies and hence, what
phase shifted horizontal synchronizing signals to trigger
successive cycles of said synchronizing signal source,
synchronizing signals, means for applying successively
and means to disable those of said phase shifted signals
10 not applied to said frame synchronizing signal source.
ever the values of the integer n.
In the illustrative embodiment, oscillator 10 has been
adjusted to a nominal frequency of 15,750 cycles per sec
3. The combination according to claim 2 in which said
phase shifting means comprises a phase-splitting trans
ond and oscillator 13 to sixty cycles per second.
former producing two signal 180 degrees out of phase
The
with respect to each other.
nominal ratio of these two frequencies is 262.5. Oscilla
4. A television scanning signal generator comprising a
tors 10 and 13, however, have been designed with a view 15
source of horizontal scanning signals, phase splitting
to simplicity and economy and hence neither has been
means, means for applying said horizontal scanning sig
more than moderately stabilized in frequency. Changes
nals to said phase splitting means, a source of vertical
in ambient conditions such as temperature and supply
scanning signals, bistable gating means, means for chang
voltage will cause these frequencies to drift. Although
the resulting ration between these frequencies will also 20 ing the state of said bistable gating means after each cycle
of said vertical scanning signal source, and means includ
tend to drift, a continuously interlaced pattern is assured
ing said bistable gating means for applying alternate
by the half cycle term added to their ratio by bistable
phases of said horizontal scanning signals to trigger said
circuit 12. It will be noted that this ratio has been greatly
vertical scanning signal source on alternate cycles of said
reduced in the waveforms of PEG. 2 for the purposes
25 vertical scanning signal source.
of clarity.
In accordance with the present invention, the simple
and compact circuit of FIG. 1 is capable of generating
a 2:1 interlaced scanning pattern for television trans
mitting apparatus. This interlaced pattern is accurately
5. A television scanning signal generator for generating
interlaced television scanning patterns comprising a source
of horizontal scanning signals producing signals at a plu
rality of equally displaced phases, a source of vertical
maintained in spite of any drift or small random ?uctua 30 scanning signals adapted to be triggered by externally
supplied pulses, and means under the control of said
tion of frequency in the horizontal or vertical oscillators.
Such a simple and economical synchronization signal gen
erator is very valuable for inexpensive television systems
such as closed circuit television and Videotelephone, where
vertical scanning signal source for successively applying
different ones of said phase displaced signals to trigger
said vertical scanning signal source.
6. The television scanning signal generator according
reasonably good resolution is desirable, but where expen 35
to claim 5 in which said trigger applying means comprises
sive and complicated circuitry is not warranted.
The invention has been illustrated in FIG. 1 with semi
conductor devices because the low power consumption
and small size of these devices makes them particularly
suitable for small, compact circuitry. It is to be under
stood, however, that the principles of the invention may be
just as readily implemented with other devices such as
vacuum tubes, vacuum diodes and so forth, merely by
choosing appropriate con?gurations for generating oscilla
tions, differentiating, phase splitting and bistable gating. 45
Similarly, it can be seen that a 3 :1 interlace or any other
interlace ratio can be similarly generated by appropriate
phase shifts in the triggering pulses and a multistable gat
ing circuit with the required number of stable conditions.
It is therefore to be understood that the above-described
arrangements are merely illustrative of numerous and
multistable circuit means having a number of stable
stages equal to the number of said phase displaced sig
nals and corresponding thereto, means for enabling the
corresponding one of said phase displaced signals when
said multistable circuit means is in each stable state, and
means responsive to said vertical scanning signal source
for changing the state of said multisable circuit means
after each cycle of said vertical scanning signal source.
7. A signal generator for generating interlaced tele
vision scanning signals comprising a source of horizontal
scanning signals, means to produce therefrom two trigger
ing signal sequences displaced in phase by 180 degrees,
a triggerable source of vertical scanning signals, and
means for alternately triggering said vertical scanning
signal generator with each of said triggering signal se
quences.
varied other arrangements which may constitute applica
8. The signal generator according to claim 7 wherein
tions of the principles of the invention. Such other ar
said triggering means includes bistable gating means to
rangements may readily be devised by those skilled in the
55
alternately disable said triggering signal sequences in
art without departing from the spirit and scope of the
response to outputs from said vertical scanning signal
invention.
generator.
What is claimed is:
1. A synchronization signal generator for use in tele
vision systems comprising a high frequency source of
References Cited in the ?le of this patent
horizontal synchronizing pulses, means for differentiating 60
UNITED STATES PATENTS
said horizontal synchronizing pulses, means for shifting
2,407,956
Hallmark ____________ __ Sept. 17, 1946
the phase of said differentiated horizontal synchronizing
2,619,632
Krumhansl __________ __ Nov. 25, 1952
pulses by 180 degrees, a low frequency source of vertical
2,730,622
Janssen ______________ __ Ian. 10, 1956
synchronizing pulses, means for triggering said low fre
Kruse ______________ __ July 29, 1958
quency source with the output of said phase shifting 65 2,845,535
means, and means controlled by said low frequency source
2,922,037
Reise _______________ __ Jan. 19, 1960
672,125
Great ‘Britain ________ __ May 14, 1952
for disabling alternate phases of said differentiated hori
zontal synchronizing pulses during alternate cycles of said
low frequency source.
FOREIGN PATENTS
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